This invention relates to an apparatus for manufacturing corner springs used with the spring structure of a mattress. The spring structure of a mattress is constructed by folding both ends of a plurality of wires 11 several times, as illustrated in FIG. 1, to form spring legs 12 at said ends, and bending the spring legs 12 in such direction as causes the spring legs 12 to be aligned with the corner sections of the spring structure. These spring legs 12 are used with the spring structure to prevent the corner sections thereof from being deformed and also to reinforce said corner sections.